We haven’t downed him yet, as we’re still trying to figure out the OMGWHATISGOINGON that is phase 4. But I’ve learned some things and drawn some pictures that might aid others.
In most cases, it’s not worth going into cat form when you’re not tanking. You lose your vengeance, the DoT does more damage, and all you can do is mangle-spam.
A bear’s gigantic passive magic reduction is pretty nice. So are Prismatic Elixirs. You can also use [Mirror of Broken Images], though it’s not necessary.
Save major cooldowns for when you have to move away from seeds in phase 2. Save minor cooldowns for when the seeds explode.
Stampeding Roar is useful when your raid needs to move away from seeds. Sadly, you can’t use it for every one (they happen once a minute).
Number the Sons of Flame from left to right; assign one person to each number. They spawn in random configurations, so this guarantees that all of them will be taken care of.
Sometimes on the second intermission, your Scion of Flame will be on the opposite side of your Son of Flame. Call this out and attempt to pull the Scion first (it will spawn a second or two before the Sons spawn). Sprint back to your Son and take care of it.
To handle the Sons of Flame, start in Bear form (while you still have vengeance) and Mangle, Maul, and Thrash. Then Bash it, go into cat form, and Shred. If your Son is about to hit the hammer, use your combo points on a Maim. If it’s still far away from the hammer, use your combo points on Ferocious Bite. When you have a Scion on you, you obviously can’t go cat form. Your raid should know this beforehand and help you with your add.
I use this spec for this fight.
Taunt at 3 stacks of Burning Wound, or as soon as your stacks fall off. Sometimes Ragnaros will apply a fourth stack on the previous tank, but there’s not a lot you can do about that.
World in Flames looks horrible but it’s really not so bad. The previous Engulfing Flames will not do damage while the current one is spawning, so what you need to do is stand somewhere close to maximum melee range and move a few yards forward and backward depending on the spawn. Ragnaros will not melee you or apply Burning Wound during this time. As a bear with overpowered magic reduction, you can survive a tick or two of Engulfing Flames (not advised).
Your whole raid should have the same version of a boss mod so that the timers are identical for everyone. We all use DBM Alpha.